Micro-oscillating member, light-deflector, and image-forming apparatus

ABSTRACT

The present invention provides a resonance type micro-oscillating member capable of retraining a fluctuation of angular velocity, and specifically provides a micro-oscillating member, which is a nested micro-oscillating member, wherein there exist a reference oscillation mode which is the characteristic oscillation mode of a reference frequency, and an even numbered oscillation mode which is the characteristic oscillation mode of a frequency being approximate even number times the reference frequency.

TECHNICAL FIELD

The present invention relates to a micro-oscillating member belonging tothe technical filed of a microstructure, and specifically to amicro-oscillating member suitable for a light-deflector, and alight-deflector using the micro-oscillating member. Further, the presentinvention relates to an image-forming apparatus, such as a scanning typedisplay, a laser beam printer, a digital copying machine, using thislight-deflector.

BACKGROUND ART

Heretofore, various light-deflectors in which mirrors areresonance-driven have been proposed. In general, a resonance typelight-deflector is characterized in that, comparing to a light scanningoptical system using a polygonal rotating mirror such as a polygonmirror, the light-deflector can be made compact to an large extent, andthe consumption power thereof can be reduced, and there exists no facetangle in theory, and particularly, a light-deflector comprising Sisingle-crystal manufactured by a semiconductor process theoretically hasno metal fatigue, and is excellent in durability (Japanese PatentApplication Laid-Open No. S57-8520).

In the meantime, in the resonance type reflector, there is a problemthat, since a scanning angle of the mirror changes in sine-wise inprinciple, an angular velocity is not constant. To correct thischaracteristic, several techniques have been proposed.

For example, in Japanese Patent Application Laid-Open Nos. H9-230276,H9-230277, H9-230278, and H9-230279, an arcsin lens is used as animage-forming optical system (image-froming lens), so that a constantvelocity scanning is realized on a scanned surface.

Further, in Japanese Patent Application Laid-Open No. 2003-279879, twopieces of deflection reflecting surfaces are driven by sine oscillationsof mutually different oscillation cycles, thereby synthesizing sinewaves and realizing an approximate constant angular velocity drivewithin a scanning range.

Further, in U.S. Pat. No. 4,859,846, by using a resonance type reflectorhaving a basic frequency and an oscillation mode of a frequency beingthree times the basic frequency, an approximate chopping wave drive isrealized.

In an electro-photography such as a laser beam printer, a laser light isscanned on a photosensitive body so as to form an image. At that time,the scanning velocity of the laser light is preferably a constantvelocity on the photosensitive body. Hence, in a light-scanning meansused in the electro-photography, it is general that, after thelight-deflector performs the scanning, an optical correction is carriedout.

For example, in the light-scanning optical system using the polygonalrotating mirror, in order to convert a light flux reflected anddeflected at the constant velocity by the deflection reflecting surfaceinto the constant scanning on the photosensitive body, an image-forminglens called as a fθ lens is used.

Further, in the light-scanning optical system using the light-deflectorfor performing a sine oscillation, in order to change a light flux inwhich the angular velocity changes in a sine wise into the constantvelocity scanning on the photosensitive body, an image-forming lenscalled as an arcsin lens is used.

However, the arcsin lens has a problem in that the size of a beam spotof the laser light on the photosensitive body changes at the time of theoptical scanning correction. In general, in the image-forming apparatus,there exist allowable upper and lower limits to the size of the beamspot allowable according to a required image quality. Therefore, in theangular velocity of the laser light emitted from the light-deflector,there exists an allowable value in the fluctuation width of the angularvelocity. Here, the upper and lower limits of the angular velocity aredenoted by θ′_(max), and θ′_(min), respectively.

Now, in the light-deflector performing the sine oscillation, adisplacement angle θ and the angular velocity θ′ can be represented bythe following formulas:θ=θ_(o) sin(ωt)  (Formula 1)θ′=θ_(o) cos(ωt)  (Formula 2)provided that θ_(o) is the maximum displacement angle, and ω is thenumber of angular oscillations. At this time, the relations ofθ′_(max)=θ_(o)ω  (Formula 3)θ′_(min)=≦θ_(o)ωcos(ω_(t))  (Formula 4)are established. FIG. 17 explains these states. In FIG. 17, the timerange satisfying the above described formulas in the vicinity of t=0 iswithin a range of:−cos⁻¹(θ′_(min)/θ_(o)ω)≦ωt≦−cos⁻¹(θ′_(min)/θ_(o)ω)  (Formula 5)and the maximum usable deflection angle θ_(eff) satisfying thiscondition and an effective time t_(eff) which is a usable time in onecycle become as follows:θ_(eff)=θ_(o) sin(cos⁻¹(θ′_(min)/θ′_(omax)))  (Formula 6)t _(eff)=2 cos⁻¹ (θ′_(min)/θ′_(max))/ω  (Formula 7)

For example, if θ′ is allowable up to ±20% for a reference angularvelocity, it becomesθ′_(min):θ′_(max)=0.8:1.2  (Formula 8)and thereby the maximum usable deflection angle θ_(eff) and theeffective time t_(eff) become as follows:θ_(eff)=sin(cos⁻¹(0.8/1.2))=0.7454θ_(o)  (Formula 9)t_(eff)=2 cos⁻¹(0.8/1.2)/(ω=1.6821%)ω  (Formula 10)In this way, there is a problem that the conventional resonance typelight defector is unable to fully obtain the maximum usable defectionangle θ_(eff) and the effective time t_(eff) as large values.

Further, there is a problem that, since the resonance type deflector hasthe same angular velocity in moving back and forth, when making a singleside scanning, the time effectively acquired for the scanning becomesshort.

Further, there is a problem that, when a plurality of deflectors areused for correcting these problems, the structure becomes complicated.

Further, there is a problem that since the mirror has to maintain adesired flatness even at the time of driving, its rigidity has to beenhanced so as to restrain the deformation of the mirror. In thelight-deflector performing the sine oscillation as in the Formula 1, theangular velocity θ″ of the mirror can be given as follows.θ″=−θ_(o)ω² sin(ωt)  (Formula 11)

In the above example, the angular acceleration becomes the maximum valueat both ends of the scanning, and the maximum value is:θ″_(max)=θ_(o)ω² sin(cos⁻¹(0.8/1.2))=0.7454θ_(o)ω²  (Formula 12)

Further, there is a problem that, when assembling a movable element anda torsion spring, it takes a lot of troubles, and moreover, it is easyto generate an assembly error.

Further, there is a problem that, when trying to make the moment ofinertia of the movable element large, it makes a miniaturizationdifficult. In the resonance type light-deflector having two or more ofmovable elements, it is most desirable that the moment of inertial ofthe movable element on which a light-deflecting element is arranged isthe smallest. However, when attempting to form movable elements and atorsion springs by working a piece of plate, in order to make the momentof inertial large, a plate having a large area is required. This becomesa barrier for miniaturization. Further, in case the movable elements andthe torsion springs are formed by the semiconductor process, a largersize of a foot print large becomes a cause of cost increase.

Further, there is a problem that, when the movable elements areconnected in series by the torsion springs, it is easy to generate notonly torsion, but also a flexure oscillation mode.

FIG. 18 is a model for explaining a flexure oscillation mode. Movableelements 1601 and 1602 are connected by a torsion spring 1611, and themovable element 1602 and a support portion 1621 are connected by atorsion spring 1612. Such a system generally has two flexure oscillationmodes. The oscillation mode form at this time is shown in FIGS. 19A and19B. FIG. 19A shows an inphase flexure oscillation mode at a lowerfrequency, and FIG. 19B shows a reverse phase flexure oscillation modeat a higher frequency. It is desirable that these oscillation modes arecontrolled as much as possible.

DISCLOSURE OF INVENTION

To solve the above-described problems, the micro-oscillating member ofthe present invention is a micro-oscillating member, comprising: aplurality of movable elements; a plurality of torsion springs arrangedon the same axis which connects the plurality of movable elements inseries; a support portion for supporting a part of the plurality oftorsion springs; driving means for applying a torque to at least one ofthe movable elements; and driving control means for controlling thedriving means,

wherein a system comprising the plurality of torsion springs and theplurality of movable elements has a plurality of isolated characteristicoscillation modes, and in the isolated characteristic oscillation modes,there exist a reference oscillation mode which is an characteristicoscillation mode of a reference frequency, and an even numberedoscillation mode which is an characteristic oscillation mode of afrequency being approximate even number times the reference frequency.

Further, in the above-described micro-oscillating member, it ispreferable that the plurality of movable elements and the plurality oftorsion springs are integrally formed from a piece of plate.

Further, in the above-described micro-oscillating member, it ispreferable that the piece of plate is a single-crystalline siliconwafer.

Further, in the above-described micro-oscillating member, it ispreferable that, when a flat plane is provided perpendicular to the axisof the torsion springs, the flat plane intersects one of the pluralityof torsion springs and at least one of the plurality of movableelements.

Further, in the above-described micro-oscillating member, it ispreferable that, when a flat plane is provided perpendicular to the axisof the torsion springs, the flat plane intersects two or more of theplurality of movable elements.

Further, in the above-described micro-oscillating member, it ispreferable that the plurality of movable elements are connected to twoof the plurality of torsion springs.

Further, the present invention is the micro-oscillating membercharacterized in that the driving control means controls the drivingmeans so as to simultaneously excite the reference oscillation mode andthe even numbered oscillation mode.

Further, in the above-described micro-oscillating member, it ispreferable that, at a driving time, an increasing time of a displacementangle of at least one of the plurality of movable elements and adecreasing time of the displacement angle are different.

Further, the light-deflector of the present invention is alight-deflector comprising the above-described micro-oscillating memberand a light-deflecting element arranged on the movable element of themicro-oscillating member.

Further, the image-forming apparatus of the present invention is animage-forming apparatus comprising the above-described light-deflector,a light source, and an image-forming optical system.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are views explaining a light-deflector of a firstembodiment;

FIG. 2 is a view explaining a resonance characteristic of thelight-deflector of the first embodiment;

FIG. 3 is a view explaining a plate member used in a light-deflector ofa second embodiment;

FIG. 4 is a graph explaining a displacement angle of the light-deflectorof the second embodiment;

FIG. 5 is a graph explaining an angular velocity of the light-deflectorof the second embodiment;

FIG. 6 is a graph explaining an image-forming apparatus of a thirdembodiment;

FIG. 7 is a view explaining a principle of a micro-oscillating member ofthe present invention;

FIG. 8 is a view explaining a principle of the light-deflector of thepresent invention;

FIG. 9 is a graph explaining a displacement angle of themicro-oscillating member of the present invention;

FIG. 10 is a graph explaining an angular velocity of themicro-oscillating member of the present invention;

FIG. 11 is a graph comparing an angular velocity of themicro-oscillating member of the present invention to an angular velocityof a sine wave driving;

FIG. 12 is a graph comparing a displacement angle of themicro-oscillating member of the present invention to a displacementangle of the sine wave driving;

FIG. 13 is a graph comparing an angular acceleration of themicro-oscillating member of the present invention to an angularacceleration of the sine wave driving;

FIG. 14 is a view explaining an effect of the present invention;

FIG. 15 is a view explaining an effect of the present invention;

FIG. 16 is a view explaining an effect of the present invention;

FIG. 17 is a view explaining an effective time of a sine wave driving;

FIG. 18 is a model explaining the flexure oscillation mode of amicro-oscillating member having a plurality of oscillation modes; and

FIGS. 19A and 19B are views explaining the oscillation mode of theflexure oscillation of the micro-oscillating member having a pluralityof oscillation modes.

BEST MODE FOR CARRYING OUT THE INVENTION

By utilizing the present invention, it is possible to restrain thefluctuation of an angular velocity in a resonance type micro-oscillatingmember. Particularly, a light-deflector of the present invention issuitable for an image-forming apparatus such as a laser beam printer, adigital copying machine.

First, reference numerals in the drawings will be described.

Reference numerals 100 and 200 denote plate members. Reference numerals101, 102, 201 to 203, 1001 to 1003, 1101, 1102, 1301, 1302, 1401, 1402,1501, 1502, 1601 and 1602 denote movable elements.

Reference numerals 111 a, 111 b, 112 a, 112 b, 211 to 213, 1311, 1312,1511, 1512, 1011 to 1013, 1111, 1112, 1411, 1412 and 1611 denote torsionsprings.

Reference numerals 121 and 221 denote support frames.

Reference numerals 1021, 1121, 1321, 1421, 1521, 1522 and 1621 denotesupport portions.

Reference numerals 131 denotes a light-reflecting film. Referencenumeral 1131 a light-reflecting element. Reference numeral 1141 drivingmeans. Reference numeral 1151 denotes driving control means. Referencenumerals 1391, 1392 and 1491 denote planes perpendicular to the axis ofthe torsion springs. Reference numeral 140 denotes an electromagneticactuator. Reference numeral 141 denotes a permanent magnet. Referencenumeral 142 denotes a coil. Reference numeral 144 denotes a yoke.Reference numeral 143 denotes a core. Reference numeral 150 denotes acontroller. Reference numeral 190 denotes a cutting line. Referencenumeral 151 denotes a reference clock generator. Reference numeral 152denotes a frequency divider. Reference numerals 153 and 154 denotecounters. Reference numerals 155 and 156 denote sine function units.Reference numeral 157 and 158 denote multipliers. Reference numeral 159denotes an adder. Reference numeral 160 denotes a DA converter.Reference numeral 161 denotes a power amplifier. Reference numeral 301denotes a light-deflector of the present invention. Reference numeral302 denotes a light source. Reference numeral 303 denotes an emissionoptical system. Reference numeral 304 denotes an image-forming opticalsystem. Reference numeral 305 denotes a photosensitive drum. Referencenumeral 311 denotes a laser light. Reference numeral 312 denotes ascanning trajectory. Reference numeral 1201 denotes θ1′ of the formula16. Reference numeral 1202 denotes θ of the formula 2. Reference numeral1211 denotes θ′_(max). Reference numeral 1212 denotes θ′_(min).Reference numeral 1221 denotes an effective time of the angular velocityθ1′. Reference numeral 1222 denotes an effective time of the sine waveθ′. Reference numeral 1231 denotes θ1 of the formula 15. Referencenumeral 1232 denotes θ of the formula 1. Reference numeral 1241 denotesthe maximum effective displacement angle of the present invention.Reference numeral 1242 denotes the maximum effective displacement angleof the sine wave. Reference numeral 1251 denotes θ1″ of the formula 15.Reference numeral 1252 denotes θ1θ of the formula 1. Reference numeral1261 denotes an angular acceleration lowering section.

FIG. 7 is a view explaining a principle of the micro-oscillating memberof the present invention. In FIG. 7, reference numerals 1001 to 1003denote n pieces of movable elements, reference numerals 1011 to 1013denote n pieces of torsion springs and reference numeral 1021schematically illustrates a support portion. The torsion springs 1011 to1013 are linearly arranged, and the movable elements 1001 to 1003 areallowed to be capable of oscillating around the torsion axes of thetorsion springs 1011 to 1013. The formula of the free oscillation ofthis system is given below. $\begin{matrix}{{{{M\overset{¨}{\theta}} + {K\quad\theta}} = 0}{{\theta = \begin{pmatrix}\theta_{1} \\\theta_{2} \\\vdots \\\theta_{n}\end{pmatrix}},{M = \begin{pmatrix}I_{1} & \quad & \quad & \quad \\\quad & I_{2} & \quad & \quad \\\quad & \quad & ⋰ & \quad \\\quad & \quad & \quad & I_{n}\end{pmatrix}},{K = \begin{pmatrix}k_{1} & {- k_{1}} & \quad & \quad \\{- k_{1}} & {k_{1} + k_{2}} & {- k_{2}} & \quad \\\quad & \quad & {\quad ⋰} & \quad \\\quad & \quad & {\quad{- k_{n - 1}}} & {k_{n - 1} + k_{n}}\end{pmatrix}}}} & ( {{Formula}\quad 13} )\end{matrix}$In the above formula, 1_(k): the moment of inertia of a movable element,k_(k): the spring constant of a torsion spring, and θ_(k): a torsionangle of the movable element (k=1, 2, . . . , n). When thecharacteristic value of M⁻¹K of this system is taken as λ_(k) (k=1 ton), the number of angular frequency ω_(k) of a characteristic mode isgiven byω_(k)=√{square root over ( )}(λk)  (Formula 14)The characteristic of the micro-oscillating member of the presentinvention is that, in these ω_(k), there are a reference frequency and afrequency which is approximate even number times the referencefrequency. The “approximate even number times” referred herein isdesirably included in the numerical value range of approximate 1.98n to2.02n (n is an arbitrary integer number) times.

As an example, the resonance type light-deflector in which the number ofmovable elements is two as shown in FIG. 8 is considered. Referencenumerals 1101 and 1102 denote movable elements, reference numerals 1111and 1112 denote torsion springs, reference numeral 1121 denotes asupport portion, reference numeral 1131 denotes a light reflectingelement arranged on the movable element 1101, reference numeral 1141denotes driving means, and reference numeral 1151 denotes drivingcontrol means. Here, supposed that I₁=1.3951E-11[kgm²],I₂=1.7143E-10[kgm²], k₁=7.91914E-03[N/m], and k₂=3.0123E-02[N/m]. Atthis time, since the characteristic value of M⁻¹K become λ₁=1.5790E08and 2=6.3166E08, the corresponding number of characteristic frequenciesbecomes ω₁=2π×2000 [Hz] and ω₂=2π×4000 [Hz]. That is, ω₂=2ω₁. Theseoscillation modes are hereinafter referred to as “mode 1” and “mode 2”,respectively.

Further, in the present invention, the driving control means 1151controls the driving means 1141 in such a way that the systemconstituting a plurality of movable elements and torsion springs isoscillated simultaneously by a reference frequency and a frequency whichis even number times the reference frequency. At that time, by variouslychanging the amplitude and the phase of the movable element of thereference frequency and the frequency which is even number times thereference frequency, various driving can be performed.

As one example, the driving control means 1141 controls the drivingmeans 1151 so that the oscillation amplitude of the movable element 1101in the mode 1 becomes 1.6a, and the oscillation amplitude of the movableelement 1101 in the mode 2 becomes 0.4a, thereby making each phasedifferent in 180 degrees. Here, “a” in the following formulas is anarbitrary constant. Since characteristic vectors corresponding to themodes 1 and 2 are v1=[1, 0.72174]^(T) and v2=[1, −0.11275]^(T), theoscillation amplitudes θ1 and θ2 of the movable elements 1101 and 1102can be given as follows.θ1=a{1.6 sin (ω₁ t)−0.4 sin(2ω₁ t)}  (Formula 15)θ2=a{1.6 (0.72174)sin(ω₁ t)−0.4(−0.11275) sin(2ω₁ t)}  (Formula 16)Since the light-reflecting element 1131 is arranged on the movableelement 1101, the movement of the light-reflecting element can be givenby θ1. Further, an angular velocity θ1′ and an angular acceleration θ1″of the movable element 1101 can be represented as follows.θ1′=aω ₁{1.6 cos(ω₁ t)−2×0.4 cos(2ω₁ t)}  (Formula 17)θ1″=aω ₁ ²{−1.6 sin(ω₁ t)+4×0.4 sin(2ω₁ t)}  (Formula 18)

θ1 and θ1′ are shown in FIGS. 9 and 10, respectively.

Next, the effects of the present invention will be described. FIG. 11 isa graph in which θ′ (1202) of the Formula 2 and θ1′ (1201) of theFormula 16 are standardized and plotted in such a way that the maximumvalues thereof become equal. In this graph, when the time of the angularvelocity present in a range between θ′_(max) (1211) and θ′_(min) (1212)is taken as an effective time, the effective time of the angularvelocity θ1′ (1201) is shown by 1221 in FIG. 11, and the effective timeof the sine wave θ′ (1202) is shown by 1222 in FIG. 11. As evident fromFIG. 11, the micro-oscillating member of the present invention has along effective time compared to the sine wave drive. Specifically, sinceθ1′_(max)=1.2×aω₁ and θ1′_(min)=0.8×aω₁, fromθ1′_(min) =aω ₁{1.6 cos(ω₁ t)−2×0.4 cos(2ω₁ t)}  (Formula 19)and 0.8=1.6 cos(ω₁ t)−2×0.4 cos(2ω₁ t)  (Formula 20),t becomes t=0, ±1/(2ω₁/π). Therefore, the effective time t1 _(eff)becomest1_(eff)={1/(2ω₁/π)−(−1ω₁/(2ω₁/π))=π/ω₁  (Formula 21).

Further, it is evident from FIG. 12 that the time of increasing thedisplacement angle θ1 (section in which the graph moves to the rightupper side) is longer than the time of decreasing the displacement angleθ1 (section in which the graph moves to the right lower side). That is,by utilizing the present invention, different from the light-deflectorof the sieve wave drive, the scanning velocity can be changed in movingback and forth. This is an advantageous characteristic in theimage-forming apparatus, which performs an image forming only when lightis scanned in one fixed direction.

FIG. 12 is a graph in which θ1 (1231) of Formula 15 and θ (1232) ofFormula 1 are plotted under the same condition as FIG. 11. When thedisplacement angle having an angular velocity present in the rangebetween θ′_(max) (1211) and θ′_(min) (1212) is taken as an effectivedisplacement angle, in this graph, since respective effective times ofθ1 (1231) and θ (1232) are shown by 1211 and 1212 in FIG. 12, themaximum effective displacement angles of present invention and the sinewave become θ1 _(eff) 1241 and θ_(eff) 1242, respectively. As evidentfrom FIG. 12, θ1 _(eff) 1241 of the present invention is larger thanθ_(eff) 1242. The θ1 _(eff) at this time can be represented as follows.θ1_(eff) =a{1.6 sin(π/2)−0.4 sin(π)}=1.6a  (Formula 22)

FIG. 13 is a graph in which θ1″ (1251) of Formula 15 and θ″ (1252) ofFormula 1 are plotted under the same condition as in FIG. 11. From FIG.13, it can be read that, in the angular acceleration lowering section1261, the absolute value of θ1″ (1251) is small compared with θ″ (1252).In case the mirror is used as the light-scanning unit, since its dynamicflexure is proportional to the angular acceleration, according to thepresent invention, when the same mirror is used, the dynamic flexurebecomes smaller. Further, when the same dynamic deflection is allowable,a mirror having a lower rigidity can be used. In general, since a mirrorhaving a low rigidity can be made light in weight, the moment of inertiacan be lowered, and the consumption power can be restrained.

Further, in the present invention, the torsion spring and the movableelement are integrally formed, so that an assembly labor can be savedand an irregularity of assembly accuracy can be eliminated.

Further, in the present invention, when the torsion spring and themovable element are integrally formed, a silicon wafer is used as amaterial, so that a Q value which is an index of the acuity of resonancecan be enhanced, and the consumption energy can be reduced.

Further, in the present invention, when a flat plane is providedperpendicular to the axis of a torsion springs, movable elements areused so that the flat plane intersects with the plurality of movableelements and torsion springs, whereby a large moment of inertial can besecured within a small area.

In FIG. 14, movable elements 1301 and 1302, and torsion springs 1311 and1312 are integrally formed from a piece of plate, and the torsion spring1312 is fixed to a support portion 1321. In this example, a plane 1391perpendicular to the axis of the torsion springs intersects with themovable elements 1302 and the torsion spring 1312, and moreover, a plane1392 perpendicular to the axis of the torsion springs intersects withthe movable element 1302 and the torsion spring 1311. By using themovable element 1302 in such a shape, an effective moment of inertia canbe obtained with a small area.

In FIG. 15, movable elements 1401 and 1402, and torsion springs 1411 and1412 are integrally formed from a piece of plate, and the torsion spring1412 is fixed to a support portion 1421. In this example, a plane 1491perpendicular to the axis of the torsion springs intersects with themovable elements 1401 and the movable element 1402. By using the movableelement 1402 in such a shape, an effective moment of inertia can beobtained with a small area.

Further, in the present invention, a plurality of movable elements aresupported by two pieces of torsion springs, respectively, so that aflexure rigidity is enhanced, and a movement of unnecessary flexure modecan be controlled. In FIG. 16, movable elements 1501 and 1502 andtorsion springs 1511 and 1512 are integrally formed from a piece ofplate, and the torsion springs 1511 and 1512 are fixed to supportportions 1521 and 1522, respectively. As evident from FIG. 16, both ofthe movable elements 1501 and 1502 are supported respectively by twopieces of torsion springs. By constituting in this way, the movement ofthe flexure mode can be controlled. Further, a plane 1591 perpendicularto the axis of the torsion springs intersects with the movable element1502 and the torsion spring 1511, and a plane 1592 perpendicular to theaxis of the torsion springs intersects with the movable element 1501 andthe movable element 1502. Similarly to FIGS. 14 and 15, even in thisshape, there is an effect of obtaining the moment of inertia with asmall area.

FIRST EMBODIMENT

FIGS. 1A and 1B are views for explaining a light-deflector of thepresent embodiment. The light-deflector of the present embodimentconsists of the micro-oscillating member and a light-reflecting film 131formed on the upper surface of a movable element 101. And themicro-oscillating member consists of a plate member 100, aelectromagnetic actuator 140 and a controller 150.

FIG. 1A is a top view of a plate member 100 formed by etching-forming asilicon wafer. A flat movable element 101 is supported up and down inFIG. 1A by two pieces of torsion springs 111 a and 111 b. A frame-shapedmovable element 102 supports the torsion springs 111 a and 111 b in itsinterior side, and is supported above and below in FIG. 1A by two piecesof torsion springs 112 a and 112 b. A frame-shaped support frame 121supports the torsion springs 112 a and 112 b in its interior side. Whilethe movable elements 101 and 102 and the torsion springs 111 and 112have two oscillation modes, their frequencies are adjusted in such a wayas to become approximately double. For example, when the moments ofinertia of the movable elements 101 and 102 are taken as I1 and I2, andthe spring constants of the torsion springs 111 a and 111 b are taken ask1/2, and the spring constants of the torsion springs 112 a and 112 bare taken k2/2, and the parameter used in the description of FIG. 8 isused, the number of two characteristic angular frequencies becomeω₁=2π×2000 [Hz] and ω₂=2π×4000 [Hz].

FIG. 1B is a schematic illustration for explaining the light-deflector.In FIG. 1B, the plate member 100 illustrates a cross section taken inthe cutting line 190 of FIG. 1A. On the upper surface of the movableelement 101, there is formed a light-reflecting film 131, and on thelower surface, a permanent magnet 141 is adhered. In FIG. 1B, the platemember 100 is adhered to a yoke 144 made of a material having a highmagnetic permeability. In the region of the yoke 144 opposed to thepermanent magnet 141, there is arranged a core 143 made of a materialhaving a high magnetic permeability, and a coil 142 is wound around thecircumference of the core 143. The permanent magnet 141, the coil 142,the core 143, and the yoke 144 constitute an electromagnetic actuator140. When the current flows into the coil 142, a torque acts upon thepermanent magnet 141, and the movable element 101 is driven.

In a controller 150, a clock signal of the frequency 2 nf generated froma reference clock generator 151 is branched into two signals, and theone signal thereof is inputted to a frequency divider 152 and becomesthe half frequency nf of the frequency 2 nf. These two signals areinputted into increment signals of counters 153 and 154, respectively.The counters 153 and 154 are digital counters, which return to zero whenreaching the maximum value n. The outputs of the counters 153 and 154are inputted to sine function units 155 and 156, respectively. The sinefunction units 155 and 156 are function units, which, when the input istaken as a X, returns the output of SIN (2πX/n). The sine function units155 and 156 generate digital sine signals of frequencies 2 f and f,respectively. The sine function units 155 and 156 have gains A and Bmultiplied by multipliers 157 and 158, respectively, and added togetherby an adder 159. The output of the adder 159 is converted into ananalogue signal by a DA converter 160, and is amplified by a poweramplifier 161, and allows to flow a current into the coil 142.

FIG. 2 is a graph in which the frequency of an alternating currentflowing into the coil 142 is plotted in the axis of abscissas and adisplacement amplitude of the movable element 101 in the axis ofordinate. In this light-deflector, there exist two characteristicoscillation modes, and moreover, the frequencies thereof are in relationof 1:2. These modes are hereinafter referred to as “mode 1” and “mode2”, respectively. The light-deflector of the present invention ischaracterized in that these two modes are simultaneously excited.

Next, a method of using the light-deflector of the present embodimentwill be described. Displacement measuring means for measuring thedisplacement of the movable element 101 is prepared to perform anadjustment. First, the generated frequency of the reference clockgenerator 151 is adjusted, and is matched to a frequency at which themovable element 101 simultaneously resonates in the mode 1 and the mode2. Next, at such a frequency, the gains of the multipliers 157 and 158are adjusted so that the amplitudes of the modes 1 and 2 of the movableelement 101 become desired values. Increment/decrement of the counter153 are performed so that the phases of the modes 1 and 2 of the movableelement 101 become desired phases. Here, the adjustment of the gains andphases may be performed in reverse order. For example, when a ratio ofthe amplitude of the mode 1 and the amplitude of the mode 2 is allowedto be 1.6:0.4, and an adjustment is made so that a phase at the scanningcenter turns in reverse, the movable element 101 is driven in such a waythat the displacement angle and the angular velocity are represented asshown in FIG. 13, respectively.

By using the light-deflector of the present invention, the lightscanning can be performed with smaller fluctuation of the angularvelocity than the conventional resonance type light-deflector.

SECOND EMBODIMENT

FIG. 3 is a top view of a plate member 200 formed by etching-working asilicon wafer. Flat movable elements 201 to 203 and torsion springs 211to 213 are alternately connected in series. The axes of the torsionsprings 211 to 213 are linearly arranged, and the other end of thetorsion spring 213 is connected to a fixing frame 221. While this systemhas three oscillation models, the frequencies thereof are adjusted so asto be in relation of approximately 1:2:3. These modes are hereinafterreferred to as “model 1”, “mode 2” and “mode 3”.

As an example, when the moments of inertial of the movable elements 201to 203 and the torsion spring constants of the torsion springs 211 to213 are I₁, I₂, I₃, k₁, k₂, and k₃, where I₁=2.0E-11[kgm²], I₂=2.0E-10[kgm²], I₃=5.0E-10 [kgm²], k₁=6.17854E-3 [Nm/rad], k₂=2.03388E-2[Nm/rad], and k₃=3.52534E-2 [Nm/rad], ${M^{- 1}K} = \begin{pmatrix}{3.08927 \times 10^{8}} & {{- 3.08927} \times 10^{8}} & 0 \\{{- 3.08927} \times 10^{7}} & {1.32587 \times 10^{8}} & {{- 1.01694} \times 10^{8}} \\0 & {{- 4.06776} \times 10^{7}} & {1.11284 \times 10^{8}}\end{pmatrix}$is established, and therefore, it is evident from the Formula 14 thatthe number of characteristic angular oscillations from the mode 1 to themode 3 become 2π×1000[rad/s], 2π×2000[rad/s], and 2π×3000[rad/s].Similarly to the first embodiment, by simultaneously exciting thesecharacteristic oscillation modes, the driving of the combination ofthese modes 1 to 3 can be performed.

FIGS. 4 and 5 are graphs showing the displacement angle and the angularvelocity of the movable element 201 when the amplitude ratio of themovable element 201 in each mode is set to 24:−6:1. The comparison ofFIGS. 5 and 10 makes it easy to see a state where a margin offluctuation of the angular velocity is made small by adding the mode 3.

In this way, by increasing the number of modes, the margin offluctuation of the angular velocity can be made much smaller.

THIRD EMBODIMENT

FIG. 6 is an example in which the light-deflector of the presentinvention is applied to the image-forming apparatus such as the laserbeam printer. A laser light 311 emitted from a light source 302 isshaped by an emission optical system 303, and is scanned by alight-deflector 301 of the present invention. An image-forming opticalsystem 304 focuses the scanned laser light on a photosensitive drum 305so as to form a spot. The scanned spot moves along a scanning trajectory312.

In the image-forming apparatus of the present embodiment, the drawing ofan image is performed in the range of an effective time t1 _(eff) shownby 1221 in FIG. 12. As evident from FIG. 11, in the light-deflector ofthe present invention, a scanning angular velocity fluctuates betweenθ′_(min) (1212 in FIG. 11) and θ′_(max) (1211 in FIG. 11) during thescanning.

When an ordinary fθ lens is used for the image-forming optical system304, the scanning velocity on the photosensitive drum 305 fluctuates. Bycontrolling a modulation clock of laser beams so as to negate thefluctuation of this scanning velocity, a correct image can be formed onthe photosensitive drum.

Alternately, it is also possible to allow the focusing optical system304 to have the characteristic of negating the fluctuation of thescanning velocity. In this case, since the diameter of the spotfluctuates, the scanning method of the light-deflector 301 may bedecided so that the margin of fluctuation of this diameter does notexceed a tolerance.

This application claims priority from Japanese Patent Application Nos.2003-430425 filed Dec. 25, 2003 and 2004-323758 filed Nov. 8, 2004,which are hereby incorporated by reference herein.

1-10. (canceled)
 11. A micro-oscillating member, comprising: a supportportion; a movable system comprising a first movable element, a firsttorsion spring which connects the first movable element to the supportportion such that the first movable element is oscillatable around anoscillating axis, a second movable element, and a second torsion springwhich connects the second movable element to the first movable elementsuch that the second movable element is oscillatable around theoscillating axis; a driving portion for oscillating the first and secondmovable elements around the oscillating axis; and a driving controlportion for controlling the driving portion, wherein the movable systemhas a reference oscillation mode which is a characteristic osillationmode of a reference frequency, and an even numbered osillation modewhich is a characteristic oscillation mode of a frequency being 1.98 ntimes or more to 2.02 n times or less the reference frequency when n isan integer of 1 or more, and wherein the driving control portioncontrols the driving portion such that the movable system simultaneouslyoscillates in the reference oscillation mode and the even numberedoscillation mode.
 12. The micro-oscillating member according to claim11, wherein the first and second movable elements and the first andsecond torsion springs are integrally formed from one piece of plate.13. The micro-oscillating member according to claim 12, wherein the onepiece of the plate is a single-crystalline silicon wafer.
 14. Themicro-oscillating member according to claim 11, wherein, at a drivingtime of the movable system, an increasing time of a displacement angleof at least one of the first and second movable elements is differentfrom a decreasing time of the displacement angle.
 15. Themicro-oscillating member according to claim 11, wherein a frequency ofthe even numbered oscillation mode is 1.98 times or more to 2.02 timesor less a frequency of the reference oscillation mode.
 16. Themicro-oscillating member according to claim 11, wherein the movablesystem further comprises a the third movable element, and a thirdtorsion spring which connects the third movable element to the secondmovable element such that the third movable element is oscillatablearound the oscillating axis.
 17. A light-deflector comprising amicro-oscillating member according to claim 11, and a light-reflectingportion provided on at least one of the first and second movableelements.
 18. An image-forming apparatus comprising: a light source foremitting a laser light; a light-deflector according to claim 17; and animage-forming optical system for forming an image on a photosensitivemember using the laser light deflected by the light-deflector.
 19. Amicro-oscillating member, comprising: a support portion; and a movablesystem comprising a first movable element, a first torsion spring whichconnects the first movable element to the support portion such that thefirst movable element is oscillatable around an oscillating axis, asecond movable element, and a second torsion spring which connects thesecond movable element to the first movable element such that the secondmovable element is oscillatable around the oscillating axis; wherein themovable system has a reference oscillation mode which is acharacteristic osillation mode of a reference frequency, and an evennumbered osillation mode which is a characteristic oscillation mode of afrequency being 1.98 n times or more to 2.02 n times or less thereference frequency when n is an integer of 1 or more.
 20. Animage-forming apparatus comprising: a light source for emitting a laserlight; a resonance type light-deflector for deflecting the laser light;an image-forming optical system for forming an image using the laserlight deflected by the resonance type light-deflector; and aphotosensitive member on which the image is formed by the laser light ofthe image formed in the image-forming optical system, wherein theresonance type light-deflector comprises: a support portion; a movablesystem comprising a first movable element, a first torsion spring whichconnects the first movable element to the support portion such that thefirst movable element is oscillatable around an oscillating axis, asecond movable element, and a second torsion spring which connects thesecond movable element to the first movable element such that the secondmovable element is oscillatable around the oscillating axis; a drivingportion for oscillating the first and second movable elements around theoscillating axis; and a driving control portion for controlling thedriving portion, and wherein an action of at least one movable elementof the first and second movable elements includes a first action ofreplacement to a first direction around the oscillating axis, and asecond action of replacement to a second direction opposite to the firstdirection, wherein the driving control portion controls the drivingportion such that a time of the first action is longer than a time ofthe second action, wherein the resonance type light-deflector reflectsthe laser light from the light source at a time of the first action, andwherein the image-forming optical system forms an image on thephotosensitive member using the laser light reflected at the time of thefirst action.
 21. The image-forming apparatus according to claim 20,wherein a modulation clock of a laser light is controlled so as tonegate fluctuation of a scanning velocity of the laser light on thephotosensitive member.
 22. The image-forming apparatus according toclaim 20, wherein the image-forming optical system has a characteristicof negating fluctuation of a scanning velocity of the laser light on thephotosensitive member.